The present invention relates generally to servoactuators for moving a load in response to a control signal, and, more particularly, to an improved redundant control actuation system in which physically-separate servoactuators, the outputs of which are connected to a common load, are cross-coupled to exchange hydraulic logic information therebetween.
Modem fly-by-wire (xe2x80x9cFBWxe2x80x9d) aircraft use hydraulically-powered electrically-controlled actuation systems, typically dual-redundant, to operate flight control surfaces, and, more recently, engine thrust-vectoring controls. As used herein, the termxe2x80x9cactuation systemxe2x80x9d refers to the total number of electrohydraulic components required to move the surface with the required functionality and performance. Many of these systems, particularly those designed for military aircraft, take the form of tandem-piston servoactuators that integrate the elements of a dual-redundant actuation system into a single mechanical package and have redundant sources supplying pressurized hydraulic fluid independently to one or more integrated electrohydraulic servovalves. On the other hand, in commercial aircraft, it is generally desired that such dual-redundant actuator systems employ physically-separated single-system servoactuators that are connected to a common load and are provided with separate connections to independent pressure sources and fluid returns.
In either case, these redundant actuation systems have been typically arranged to operate cooperatively. More particularly, the servovalves have been typically connected with respect to their respective actuators with logic valves that permit three distinct operating modes for each operable half of a dual servoactuator or for each single-system servoactuator. The first of these modes involves active control, in which the servovalve is used to actively control the flows of fluid with respect to the associated actuator. The second mode is known as a free-bypass mode, in which the actuator is effectively disconnected from its associated servovalve (e.g., because its control elements or power supplies have failed) to permit continued control and operation of the load by the other servoactuator. The third is known as a fail-safe mode, in which the servovalve is disconnected from the associated actuator, and in which the opposing chambers of the disconnected actuator communicate with one another through a restricted orifice to permit continued, albeit xe2x80x9cdampedxe2x80x9d, movement of the load.
Previous cross-coupling techniques for redundant servoactuators have employed the exchange of electrical and/or hydraulic signals. In general, these prior art devices have involved pilot-operated solenoid valves and fail-safe valves to accomplish mode switching in response to certain conditions. Some devices have even employed a bypass valve in connection with a fail-safe valve. Upon information and belief, each of these prior systems has involved a compromise of performance, weight, size or expense.
Accordingly, it would generally be desirable to provide an improved redundant control actuation system, and servoactuator for use in same, that avoids these compromises in the prior art.
With parenthetical reference to the corresponding parts, portions or surfaces of the embodiment disclosed in FIGS. 4 and 4A, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved servoactuator (101A) for use in a redundant control actuation system (100), and an improved redundant control actuation system employing such servoactuators.
The improved servoactuator has a body and broadly includes: a control valve (102A) mounted on the body and arranged to provide a hydraulic output in response to a control signal; a hydraulic actuator (106A) mounted on the body and arranged to move a load in response to the hydraulic output from the control valve; and logic valve means (103A, 104A, 105A) mounted on the body and operatively associated with the control valve and actuator. The body communicates with a source of pressurized fluid (PS1) and with a fluid return (R1). The body is also provided with an external hydraulic signal. The logic valve means is supplied with such hydraulic signal and with electrical input signals, and is operatively arranged between the control valve and the actuator to either (a) control operation of the actuator in response to the control signal, (b) permit the actuator to move freely and independently of the control signal, or (c) restrain movement of the load independently of the control signal. The selected mode is a function of the supplied hydraulic and electrical input signals. The logic valve means is operatively arranged to provide a hydraulic output signal external of the body which is a function of the supplied hydraulic and electrical signals.
The improved redundant control actuation system (100) broadly comprises: first and second servoactuators (101A, 101B), each servoactuator having a body and having: a control valve (102A, 102B) mounted on the associated body and arranged to provide a hydraulic output in response to a control signal; a hydraulic actuator (106A, 106B) mounted on the associated body and arranged to move a load in response to the hydraulic output from the associated control valve; and logic valve means (103A, 104A, 105A, 103B, 104B, 105B) mounted on the associated body and operatively associated with the control valve and actuator. The associated body communicates with a source of pressurized fluid (PS1, PS2) and with a fluid return (R1, R2), and is provided with an external hydraulic signal. The logic valve means of each servoactuator is supplied with such hydraulic and electrical input signals, and is operatively arranged between the associated control valve and actuator to either (a) control operation of the actuator in response to the control signal, (b) permit the actuator to move freely and independently of the control signal, or (c) restrain or impede free movement of the load independently of the control signal. The selected mode is a function of the supplied input signals. The logic valve means of each servoactuator is arranged to provide a hydraulic output signal external of the associated body which is a function of the hydraulic and electrical signals. The hydraulic output signal of one servoactuator is provided as the hydraulic input signal to the other servoactuator.
In the preferred embodiment, each control valve (102A, 102B) is an electrohydraulic servovalve, and the two servovalves are identical.
Each servoactuator (101A, 101B) may further include a first flow passageway arranged to selectively communicate the opposing chambers of its associated actuator when its logic valve means permits the actuator to move freely and independently of the control signal. Each servoactuator may further include a second flow passageway having a restricted orifice (115A, 115B). The second flow passageway is arranged to selectively communicate the opposing chambers of its associated actuator when its logic valve means causes the actuator to restrain movement of the load independently of the control signal.
The logic valve means may include a bypass valve (104A, 104B) and a fail-safe valve (105A, 105B) connected hydraulically in series between the associated control valve (102A) and actuator (106A). The bypass valve is movable between a first position in which fluid is permitted to flow between the associated control valve and actuator, and a second position in which fluid is prevented from flowing therebetween and is freely bypassed (i.e., without purposeful flow restriction) between the opposing chambers of the associated actuator. The bypass valve may be biased toward the second position. The bypass valve may include a valve spool (110A, 110B) mounted for sealed sliding movement within a body, and may further include a spring (111A, 111B) operatively arranged to cause the spool to move toward the second position. The spool may be caused to move toward the first position by a fluid pressure.
The servoactuator may further include a port to which an external source of pressurized fluid (PS1) is supplied, and a solenoid valve (103A, 103B) operatively arranged between the port and the bypass valve. The solenoid valve may communicate with the port and be arranged such that energization of the solenoid valve by the electrical input signal will cause pressurized fluid from the port to move the bypass valve spool (110A, 110B) to the first position and to provide the hydraulic output signal.
The fail-safe valve (105A, 105B) is movable between an open position in which fluid is permitted to flow between the associated bypass valve and the actuator, and a closed position in which fluid is prevented from flowing between the associated bypass valve and actuator. The fail-safe valve may be biased toward its closed position. The fail-safe valve may further include a valve spool (112A, 112B) mounted for sealed sliding movement within a body, and a spring (113A, 113B) operatively arranged to cause the fail-safe valve spool to move toward its closed position. A fluid pressure, supplied to the servoactuator as its hydraulic input signal, may urge the fail-safe valve spool to move toward its open position.
Accordingly, the general object of the present invention is to provide an improved servoactuator for use in a redundant control actuation system.
Another object is to provide an improved redundant control actuation system employing two such servoactuators.
Still another object is to provide an improved redundant control actuation system which employs hydraulic logic cross-coupling between physically-separate redundant servoactuators to allow each servoactuator three modes of operation, as appropriate, without electrical cross-coupling between them.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims.